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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 29 April 2008 by Barry Brook

Guest post by Barry Brook, Director of the Research Institute for Climate Change and Sustainability at the University of Adelaide. Read more at Brave New Climate.

Human are transforming the global environmental. Great swathes of temperate forest in Europe, Asia and North America have been cleared over the past few centuries for agriculture, timber and urban development. Tropical forests are now on the front line. Human-assisted species invasions of pests, competitors and predators are rising exponentially, and over-exploitation of fisheries, and forest animals for bush meat, to the point of collapse, continues to be the rule rather than the exception.

Driving this has been a six-fold expansion of the human population since 1800 and a 50-fold increase in the size of the global economy. The great modern human enterprise was built on exploitation of the natural environment. Today, up to 83% of the Earth’s land area is under direct human influence and we entirely dominate 36% of the bioproductive surface. Up to half the world’s freshwater runoff is now captured for human use. More nitrogen is now converted into reactive forms by industry than all by all the planet’s natural processes and our industrial and agricultural processes are causing a continual build-up of long-lived greenhouse gases to levels unprecedented in at least the last 800,000 years and possibly much longer.

Clearly, this planet-wide domination by human society will have implications for biological diversity. Indeed, a recent review on the topic, the 2005 Millennium Ecosystem Assessment report (an environmental report of similar scale to the Intergovernmental Panel on Climate Change Assessment Reports), drew some bleak conclusions – 60% of the world’s ecosystems are now degraded and the extinction rate is now 100 to 1000 times higher than the “background” rate of long spans of geological time. For instance, a study I conducted in 2003 showed that up to 42% of species in the Southeast Asian region could be consigned to extinction by the year 2100 due to deforestation and habitat fragmentation alone.

Given these existing pressures and upheavals, it is a reasonable question to ask whether global warming will make any further meaningful contribution to this mess. Some, such as the sceptics S. Fred Singer and Dennis Avery, see no danger at all, maintaining that a warmer planet will be beneficial for mankind and other species on the planet and that “corals, trees, birds, mammals, and butterflies are adapting well to the routine reality of changing climate”. Also, although climate change is a concern for conservation biologists, it is not the focus for most researchers (at present), largely I think because of the severity and immediacy of the damage caused by other threats.

A large number of ancient mass extinction events have indeed been strongly linked to global climate change, including the most sweeping die-off that ended the Palaeozoic Era, 250 million years ago and the somewhat less cataclysmic, but still damaging, Palaeocene–Eocene Thermal Maximum, 55 million years ago. Yet in the more recent past, during the Quaternary glacial cycles spanning the last million years, there were apparently few climate-related extinctions. This curious paradox of few ice age extinctions even has a name – it is called ‘the Quaternary Conundrum’.

Over that time, the globally averaged temperature difference between the depth of an ice age and a warm interglacial period was 4 to 6°C – comparable to that predicted for the coming century due to anthropogenic global warming under the fossil-fuel-intensive, business-as-usual scenario. Most species appear to have persisted across these multiple glacial–interglacial cycles. This can be inferred from the fossil record, and from genetic evidence in modern species. In Europe and North America, populations shifted ranges southwards as the great northern hemisphere ice sheets advanced, and reinvaded northern realms when the glaciers retreated. Some species may have also persisted in locally favourable regions that were otherwise isolated within the tundra and ice-strewn landscapes. In Australia, a recently discovered cave site has shown that large-bodied mammals (‘megafauna’) were able to persist even in the arid landscape of the Nullarbor in conditions similar to now.

However, although the geological record is essential for understanding how species respond to natural climate change, there are a number of reasons why future impacts on biodiversity will be particularly severe:

B) A low-range optimistic estimate of 2°C of 21st century warming will shift the Earth’s global mean surface temperature into conditions which have not existed since the middle Pliocene, 3 million years ago. More than 4°C of atmospheric heating will take the planet’s climate back, within a century, to the largely ice-free world that existed prior to about 35 million years ago. The average ‘species’ lifetime’ is only 1 to 3 million years. So it is quite possible that in the comparative geological instant of a century, planetary conditions will be transformed to a state unlike anything that most of the world’s modern species have encountered.

C) As noted above, it is critical to understand that ecosystems in the 21st century start from an already massively ‘shifted baseline’ and so have lost resilience. Most habitats are already degraded and their populations depleted, to a lesser or greater extent, by past human activities. For millennia our impacts have been localised although often severe, but during the last few centuries we have unleashed physical and biological transformations on a global scale. In this context, synergies (positive or self-reinforcing feedbacks) from global warming, ocean acidification, habitat loss, habitat fragmentation, invasive species, chemical pollution (Figure 2) are likely lead to cascading extinctions. For instance, over-harvest, habitat loss and changed fire regimes will likely enhance the direct impacts of climate change and make it difficult for species to move to undamaged areas or to maintain a ‘buffer’ population size. One threat reinforces the other, or multiple impacts play off on each other, which makes the overall impact far greater than if each individual threats occurred in isolation (Brook et al 2008).

D) Past adaptation to climate change by species was mainly through shifting their geographic range to higher or lower latitudes (depending on whether the climate was warming or cooling), or up and down mountain slopes. There were also evolutionary responses – individuals that were most tolerant to new conditions survived and so made future generations more intrinsically resilient. Now, because of points A to C described above, this type of adaptation will, in most cases, simple not be possible or will be inadequate to cope. Global change is simply too pervasive and occurring too rapidly. Time’s up and there is nowhere for species to run or hide.

Professor Barry Brook is an international research leader in global ecology and conservation biology. He holds the Foundation Sir Hubert Wilkins Chair of Climate Change and is Director of the Research Institute for Climate Change and Sustainability at the University of Adelaide. He has published two books and over 120 scientific papers on various aspects of human impacts on the natural environment and biodiversity, including climate change, deforestation and overexploitation of populations. In 2006, he was awarded both the Australian Academy of Science Fenner Medal for distinguished research in biology and the Edgeworth David Medal by the Royal Society of New South Wales, and in 2007, the H.G. Andrewartha Medal by the Royal Society of South Australia and was listed by Cosmos as one of Australia's top 10 young scientists. The principal motivation for his research is to identify ways and means of reducing extinctions and mitigating the worst ravages of global change.

Comments

Excellent post. Extinction cycles and their causes are one of my favorite studies. An extinction cycle weeds out less adaptive species and creates diversity amongst the more flexible species. It should be interesting to see P.E. in action. In fact we may already have seen it in some of those newly discovered species in the same area of the world. This could be a very interesting thread.

Quietman, what's P.E.? You seem to be promoting the idea that extinction is "good" because it improves opportunities for the surviving species. Although it's obvious that niches that have been opened invite evolutionary explosions among surviving lineages, I think it's unclear that extinctions are "good". Before I get too worked up about it, I should ask exactly what you mean. I should also ask what you mean about newly discovered species. Are you talking about new speciation events or new description of products of ancient speciations?

Steve L
P.E. is the Punctuated Equilibrium hypothesis put forth to exolain rapid changes in evolution on the species level. In Gould's view mutations occur under stressed conditions more rapidly, increasing diversification. In this view, while the parent species may become extinct, its offspring live on as several new species, of which at least one lineage has a higher probability of survival. In this light, there is no net loss, only change.

["P.E. is the Punctuated Equilibrium hypothesis put forth to exolain rapid changes in evolution on the species level. In Gould's view mutations occur under stressed conditions more rapidly, increasing diversification. In this view, while the parent species may become extinct, its offspring live on as several new species, of which at least one lineage has a higher probability of survival. In this light, there is no net loss, only change."]

I'm not sure that's a good description of Punctuated Equilibrium for several reasons, and you seem to be (correct me if I'm wrong) pursuing the notion that man-made extinctions (present and future), are a rather jolly wheeze from the point of view of interesting potential observations (your first post seems to indicate that).

Here's some of the problems:

1. It's unlikely that mutations occur more rapidly under stressed conditions, if by "mutations" you mean the DNA-level mutations that underpin the evolutionary process.

2. Eldredge and Gould, as far as I remember, didn't specify "stressed conditions" in relation to P.E. The main mechanistic element of P.E. is the existence of sub-populations of species, either at the physical margins of the population range, or completely isolated from the main species population. In these instances mutations don't occur more rapidly. However mutations are not diluted through the main species pool, and so may be maintained in the sub-population. In fact speciation within P.E. might occur by genetic drift. The major element is population-isolation rather than population-stress.

3. P.E. is neutral with respect to diversification. P.E. scenarios resulting in increased diversification can be formulated (there's evidence for these) as can P.E. scenarios resulting in none, or even decreased diversification (there's evidence for these too) although the latter would involve more widespread consideration of a particular ecosystem.

The latter is the concern with respect to global warming within a world with already fragmented and denuded ecosystems as indicated in the excellent summary by Barry Brook at the top of this section.

Clearly over the significant human-scale term (10's, 100's, 1000's of years) exctinctions are going to continue to increase, so (whatever the joys of potentially "observing" P.E. on the hoof!), we're not going to see diversification. Secondly, it's not obvious that we're likely to have enhanced opportunities for observing P.E. on the hoof anyway. In fact the opposite is far more likely. Never mind the fact that speciation events require many generations, and so we're unlikely to see these in animals on human timescales anyway. In a world of fragmented and denuded ecosystems there are likely to be less speciation events to observe. After all we can already observe incipient speciation under P.E. type scenarios (e.g. "ring species"), and it's questionable whether things are going to be more interesting in that respect in a world with even higher levels of species extinction.

The comment is about how the species will adapt as was specified in the title to the blog. So adaptation, not extinction is the subject (no offense meant).

My remark about it being interesting is simply that I have studied paleontology, extinction and evolution for over 40 years as a hobby so I appreciate a Blog on my favorite subject.

P.E. was actually a Darwinian conceot that he mentioned in "On the Origin of Species". Both Darwin (in his writings) and Gould (in TV intervies) spoke about environmental pressures causing sudden jumps in evolution, and that is the part of PE that I refer to.

The most recent study of extinction cycles is out of USC Berkely and they found an average rate of 62 million years. This should place us within the error bounds of an extinction cycle right now which seems to have begun about 10,000 years ago, the cause of which is climate change, as is the end cause of every major extinction regardless of the trigger mechanism.

Extinction of a species happens constantly, its natural and the species is replaced by something else. An example is the polar bear, not a true species by definition, but a variation of the grissly bear. The Species is not endangered but a variation or subspecies is. That is how evolution works, although the polar bear is not actually in danger of extinction and the likely result will be hybrisization.

What I found interesting is not the extinction but the new species cropping up in the more tropical climates. especially SE Asia and South America. They are new discoveries but are they small populations because of an extinction or because they are brand new species of the Holocene? I wait with anticipation for the DNA results.

None of this is heartless or cruel, its just how nature works.

00

Response: The article is about extinction. The premise is "will animals adapt or become extinct". In fact, the original title was "will global warming cause a mass extinction event?" but I changed it. Now wondering if I was mistaken.

I have to disagree on this point. We have already seen diversification within the Holocene. The same Polar/Grizzly Bear exaample serves. It is one species that we did not recognize as one because they were/are in the process of speciation (Darwin's mutation and variation in isolation). Hybridization is already showing up as their habitats begin to overlap. Hybridization can lead to a new subspecies as well. If subsequently isolated speciation would occur eventually as well.

The comparison of the geologically short time that hominids have existed can not be validly compared to the thousands of years prior. If you want to use the past century, it needs to be compared to a similar sized slice of the past. This is a common error when trying to compare trends. The likelyhood of the slope of a single century resembling that of an epoch is extremely low. Its like apples and oranges, they both may be round but there the similarity ends.

Quietman, I have an interest in evolution too and work as a biologist studying salmonids. I say that because I think I disagree with large portions of what you've written, and I don't want you to think it's because of a lack of evolutionary perspective on my part. One place we could start is with polar vs grizzly bears. I pick this one because it's topical wrt an impending decision re ESA listing. (Is that why you chose that example?) First argument: Ursus arctos vs Ursus maritimus -- they are described as distinct species; hybridization is not enough to say they are only subspecies unless you apply a strict "biological species concept" (Mayr). You can search for many articles describing the difficulties in applying that concept. You might like to read this paper, too (I'm a coauthor): http://tinyurl.com/5fdax5
Second argument: under the ESA, distinct population segments can be listed as species. That is, the legal definition of species does not follow the biological species concept.

You can't separate adaptation from extinction in the context of global warming. If the title of the thread is "Can animals and plants adapt to global warming?" the answer must contain the probability that for many species the answer will be no. No means extinction. There's rather clear from Barry Brook's analysis and from what we have observed already in relation to habitat destruction and impoverishment.

There's no such thing as an "extinction cycle". There are extinction events that have causes (most likely climatic changes in the broadest sense as you indicate). So the Holocene extinction is not part of some grand "cycle", and describing it as such can suggest the notion that it's either inevitable or nothing of much concern (after all it's just another part of the "extinction cycle"!) In fact it's an extinction that relates to man-made destruction and impoverishments of habitats, and it's likely to be exacerbated in a warming world. It is an issue that we can choose to address or not.

I don't see your point about diversification in relation to polar and grizzly bears. Of course species have diversified in the past (polar bears likely split from the ancestral species from a couple of 100,000 years ago). The past has seen a glorious diversification of species to give us the richness of the natural world which man-kind has already rather significantly reduced especially during the last couple of centuries. If one considers the fate of bears now and in the future it's not a rosy one. For example, the possibility that polar bears become extinct as their habitat disappears in a warming world is a significant one. Unless wilderness areas are maintained there won't be any bears at all, since bears and mankind are incompatible outside of zoo's and circus's...considering bears overall, extinction is a rather more likely future than diversification...

That's really the point. In the deep past speciation/diversification occurred with speciation events likely taking 100's of 1000's of years (much like the polar bear speciation/diversification). Every so often massive climate change (resulting from extraterrestrial impacts or from massive tectonic events, for example) resulted in very widespread extinctions. These events weren't associated with diversification since, in general, most of the species of interest were unable to adapt. They went extinct without diversification. It was only following the recovery to more stable environments that the evolutionary process allowed the recovery of an impoverished post-cataclysmic biosphere, and this recovery, which was associated with rather widespread speciation/diversification as habitats were repopulated took many millions of years.

So we need to be clear about where we are. Yes we have seen some speciation/diversification during the Holocene (the evolution of freshwater seals in Finland is a better example, since this is a truly post-glacial event), but we've seen far more extinction. The combination of continued habitat destruction combined with a very rapid warming is very likely to see this trend accelerating into the future. Yes there will be many species that survive and a few may diversify in response to habitat/climatic changes in the coming 100's and 1000's of years. But on the whole the biosphere will continue to become impoverished. If we have 500,000 species of "interesting animals" (say the size of a child's fist and larger!), and we watch 200,000 of these disappear (unable to adapt = extinct), while 100 (say) undergo diversification to new species, I think we would agree that the richness and diversity of the biosphere has become degraded.

In recognising where we are, we have the ability to address these issues, since we're very much part of it all. We're not bystanders observing some inevitable "extinction cycle" and 'though we might be enthused by the possibility of P.E.-type diversification within those species that are able to adapt to an impoverished natural world, I would consider that future generations would be rather more enthused by the possibility that we might now be taking steps to minimize the impoverishment of the natural world which they will inherit.

Steve L
I understand what you are saying, there is more than one definition. I database fossil species primarily so I look at living species from a evolutionary point of view. I see polar bears as speciation in progress, so calling them a species as far as legal terms go, I don't have an issue with and that is not why I used them. I used polar bears because everyone is somewhat familiar with them on an international level. Coyotes are not as well known but are another example of speciation in progress.

I do not disagree that there is a possibility of these extinctions. But I do feel that in most cases diversity must and will occur, just as descibed by Darwin, but that it will be new species that survive, not the parent species.

Re: "There's no such thing as an "extinction cycle"."
That is not a fact. It has not been proven one way or the other. The Berkeley paper is a hypothesis, and if correct, we are in one now. The evidence so far is very good that we indeed are. Are you denying that there are climate cycles as well?

I agree with your closing statement. We should indeed protect the environment to minimize stress on these animals, but that does not make it less interesting from an evolutionary standpoint.

By the way, I am somewhat skeptical about the current causes of climate change. So from my point of view much of this is natural. But that is irrelevant to my statements here, as I am not advocating that we just let them die. So please do not be offended by my scientific curiosity.

["I do not disagree that there is a possibility of these extinctions. But I do feel that in most cases diversity must and will occur, just as descibed by Darwin, but that it will be new species that survive, not the parent species."]

I think you're being over-theoretical here. If one dissociates oneself from extant reality and views our situation as an interested bystander, no doubt one can conclude that the present extinction period, will in time (we're talking many 100's of 1000's to millions of years), result in a rediversification of life on Earth. All very interersting from a Darwinian perspective no doubt.

However if we are interested in our extant reality and that of our descendants over the next decades, 100's and even 1000's of years, then we might want to put those academic considerations aside and focus on the reality. And the reality is that continued habitat degradation exacerbated by continued global warming is going to produce an inpoverished biosphere.

Since we're not disinterested bystanders, but are in fact an integral causal part of these processes, we might want to consider doing something to address the problem (which we are, as it happens, since there are many efforts underway to protect wilderness areas, and there are growing efforts to address the problems of man-made global warming).

["Re: "There's no such thing as an "extinction cycle"."
That is not a fact. It has not been proven one way or the other. The Berkeley paper is a hypothesis, and if correct, we are in one now. The evidence so far is very good that we indeed are. Are you denying that there are climate cycles as well?"]
Fair enough. However one has to be careful here. Let's say that the Berkeley paper [Rohde and Muller, Nature 434, 208 (2005] is correct. You say that means that (referring to extinction "cycles") "...we are in one now. The evidence so far is very good that we indeed are".

But that is to take the passive attitude to ridiculous extremes. The natural world is not in the process of undergoing a large-scale extinction because of some ill-defined, uncharacterised "cycle" in which we find ourselves helplessly unlucky enough to find ourselves!. It is in the process of large-scale extinction because of large-scale habitat destruction and the other human practices described in Barry Brook's article at the top of this thread. We're part of it.

Now are there extinction cycles? Perhaps there are but the evidence isn't very strong. It's possible that the extinction/diversity events only appear to follow a cycle, but aren't cyclic at all. After all there's rather good evidence that the end-Cretaceous extinction
65.5 million years ago (mya) was due to an extra-terrestrial impact perhaps supplemented by the massive tectonic events which formed the Deccan Traps in now-India. The extinctions at the Paleo-Eocene Thermal Maximum (55 mya) was likely due to the tectonic events (and massive release of methane) associated with opeining up of the North Atlantic plate boundary. The Triassic-Jurrasic extinction (201.6 mya) associates with the massive volcanic outpourings of the central Atlantic magmatic province.....The huge Permian-Triassic extinctions (252.5 mya) appear to coincide with the tectonic events resulting in the Serbiamn Traps formation....and so on.

Are these events part of some huge cyclic phenonenon during Earth's history? It seems unlikely. The most "popular" notion of the origin of the 62 my "cycle" is long term cyclic variation of the cosmic ray flux (CRF). But how does that relate to tectonic events on Earth? It's difficult to ascribe any sort of connection.

I suspect that the extinction/diversity cycles only appear to be "cyclic". However even if they truly are part of a grand cycle, that obviously doesn't account for the current extinctions. Is the world undergoing massive tectonic processes during the past 200 years? No. Are we being blasted by a massively enhanced CRF all of a sudden. No.

We know what is causing the current extinction. It ain't some magical "cycle". It would be foolish to sit back passively and suggest such a thing...

["Are you denying that there are climate cycles as well"]

Which "climate cycles"? There is an 11 year solar cycle. There seem to be cycles associated with ocean circulation. There are the climate cycles associated with the slow variations in the orbital properties of the Earth (Milankovitch cycles). But what other cycles are you considering? Again the same argument applies. Whether or not there are "climate cycles", we know that the current very marked warming of the last 30-odd years isn't due to any of the cycles that we know of. It's very likely to be due to man-made enhancement of the Earth's greenhouse effect.

By suggesting that everything is "natural" (we're in a "natural extinction cycle"; we're in a "natural warming cycle") we might conveniently absolve ourself from any imperative to address these problems. In fact we know with a very high degree of probability that the current extinctions are not part of some "natural cycle" and the the current warming is not part of some "natural cycle". The evidence is overwhelming on the first and very strong on the second.

Clearly if these were "natural" then the must have some explanation in terms of "natural phenomena". So what are these "natural phenomena"?

John
In your comment to chris you mrntion a title change. I think that you chose the better title as AGW may make the event worse but did not start the event which has been going on for a very long time. We, as a species, have only barely survived this event and are in a diversification stage ourselves. My personal belief is that this event is nearing an end and we will be the winners if we get our act together.

chris
You are asking me to give an answer that that thus far has been unanswerable. I can only give you my philosophical view.

For starters, my view of our part in extinctions is a natural one. We are animals struggling for survival. In our struggle we have made many mistakes and to correct them is the obvious thing to do. But because we are a part of nature the term "man made" warming is referring to our mistakes and not outside of nature.

The current AGW is the point of contention. Will it cause extinction on its own. No, I do not feel that our errors alone are a cause but they certainly don't help.

Should we save the polar bears, No. First, I don't believe that they need any help. Second, they are a competitor to us as a species, we eat the same food and occupy the same habitat. Our duty is to our species, not to a species in competition. The save the bears thing is an emotional issue, not a darwinian issue. We need to concentrate on helping species that are beneficial to us, regardless of the actual cause of their stress.

As for the cyclic nature of the universe, that would take a lot more room than John has on this server. We need to stay on a point to point basis, like PDO and the Atlantic cycles, the vulcanism and gravitational pressure that drive them and the solar cycles, each has a place but not in this thread.

But the dinosaurs were already in decline before the Yucatan impact and before the eruption of the Deccan Traps due to a cooling climate which they could not adapt to. Their problem was that Dinosaurs Probably Lacked Tissue To Generate Heat *2. Vulcanism and the impact pushed them over the edge.

There are a lot of forcing cycles for climate change and for extinctions vulcanism and impact cycles also must be included (see Johns PDO title, the solar titles and the volcanos title for just a few).

*1 Adapted from materials provided by Cardiff University
*2 Adapted from materials provided by New York Medical College

There are two issues here. One is the reality of our present impact on the biosphere and the additional consequences of global warming on a natural world suffering the effects of habitat destruction and fragmentation. That's what Barry Brook's article is about.

The second is about the causes of previous extinctions and the possibility of cyclic causal factors. These can be addressed separately, since while past extinctions are clouded in various uncertaintites, the present extinction is not.

So I'll address the current extinction in this post and the possibility of cyclic contributions to past extinctions in another. Notice that the possible contributions to past major extinctions are (whether cyclic or not) variously: tectonic events; catastrophic extraterrestrial impacts; changes in greenhouse gas concentrations (CO2; methane) resulting in global warming or cooling that may be associated with tectonic events or impacts; sea level changes; variations in the cosmic ray flux...(we might come up with some others...)

NONE of these apply to the current extinction event even 'though the enhanced greenhouse contribution is likely increasingly to do so (that's the subject of this thread if you remember!). The last several thousand years, and especially the last several hundred years has NOT seen extinction-level tectonic events, extraterrestrial impacts, massive sea level changes, very large and persistent changes in the cosmic ray flux; large changes in greenhouse gas levels and so on...

So the current extinctions are not a consequence of any of these, nor a consequence of any unspecified grand "cycles". They’re a result of mankind’s impacts on the biosphere, especially habitat destruction and fragmentation. Let's not pretend that we don't know what we do know!

The problem with the attempt at passive dissociation from these realities is that it leads to a rather disinterested acceptance of events that might very well be in our control to address. So let's look at these:

(i) You consider that our part in these processes (direct extirpation of species by hunting or persecution; habitat destruction and fragmentation; more recently, massive release of greenhouse gases) is a natural one. That certainly applies in the past; however not only is that an unhelpful notion in the present context (it lends to passive acceptance of issues we might otherwise address productively), but at some point that notion breaks down, at the very least at whatever time in our history we start to recognise the wider consequences of our actions, and it’s implications for our futures. So it’s not really “natural” anymore by most generally recognized meanings of the term.

But however we might semanticize our present situation ("natural"/"non-natural"), the fact is that we might decide to address the problems since we recognise and understand these. We might choose to address policy that limits destruction of habitats and allows these to extend somewhat; we might take further measures to protect ocean species by setting up protected no-fishing respite zones in the manner that is being undertaken already; we might take measures to limit greenhouse gas emissions, and to curb human population growth...in fact we have to do some of these sooner or later…the only meaningful long term future for mankind is one based on stable populations in societies fueled by renewable energy sources for example, and that future starts rather soon!

(ii) you suggest that we shouldn't "help" polar bears since they’re apparently a "competitor to us as a species" and "we share the same habitat" and "eat the same food" and "we should concentrate on saving species that are beneficial to us". Fair enough...but what a dismal philosophy if I may say so. After all why not kill off all species that we can't productively convert into domesticated animals for food, furs, milk, and other bits and pieces? And in what way is the polar bear a "competitor" which "shares or habitat" (Arctic continental margins and sea ice?) and eats the same food (seals?)? Mankind has co-existed pretty comfortably with polar bears and there's no reason why we can't continue to do so. It may be that the polar bear is doomed because its habitat is not going to survive the likely destruction of Arctic sea ice. But let’s recognize that that will be a diminishing prospect for us and the natural world and one that we might take careful note of, especially in relation to more effective protection of wilderness areas.

There is a philosophical issue here of which Barry Brook’s article highlights one side and your posts highlight a rather extreme other. On the one hand, we can make mature and rational attempts to inform ourselves about the natural world, our place within it and our impacts, as indicated by careful observations and analysis, and then address these in relation to concerns about our wellbeing and that of our near descendants (who will themselves have to address these issues)…

..or on the other hand, we can sit back and wash our hands of the whole affair, using as justification for our passivity, pseudoscience notions of “natural” “cycles”, which we are apparently helpless to explain and understand.

Hunting around for the latest press releases and popular science articles as all-encompassing “explanations” for past events isn’t very helpful or scientific. Scientific explanations require a set of rather more self-consistent data and theoretical frameworks. A very recent paper that indicates that dinosaurs may not have had the genes for generating brown adipose tissues (the article in Science Daily that you urled), does not suddenly become the explanation for the demise of the dinosaurs, let alone the more widespread extinctions associated with the end-Cretaceus events! The possible lack of adipose tissue in dinosaurs certainly wasn’t the cause of end-Cretaceous extinction of ammonites, mosasaurs, plesiosaurs, various birds and mammals, plants and invertebrates, and so on..

In fact, if you read the paper referred to in your popular news article [N. V. Mezentseva et al (2008) “The brown adipocyte differentiation pathway in birds: an evolutionary road not taken”; BMC Biology 6 (17) 21 April 2008], you’ll see that the authors don’t mention dinosaur extinction at all (the words “extinct” or “extinction” don’t appear in their paper). No doubt the popular press article that you urled was “sexed up” by an editor to give it a punchy general appeal.

The fact is that the end Cretaceous extinctions were not due to the possible lack of brown adipose tissue in dinosaurs, although that might or might not have contributed to the demise of that particular order. Regarding the dinosaurs, it’s rather more likely that the widescale attenuation of photosynthetic activity for a few years following an extraterrestrial impact was more than sufficient to kill off large herbivores and their predators. For the extinction event overall, the evidence indicates a combination of an extraterrestrial impact with a long term tectonic events associated with the Deccan Traps formation in non-India as the likely causal factors [e,g Beerling et al (2002); Keller (2005); Kelley (2007)].

But was the end-Cretaceous extinction part of a regular “cycle” of extinctions? The evidence isn’t very strong. You describe Wikramsinghe and Napier as indicating a 36 million year (my) cycle of extraterrestrial impacts that relate to passage of the solar system through the galactic plane. That paper isn’t available yet apparently, but a recent similar study by Napier [“evidence for cometary bombardment episodes” Mon. Not. R. Astron. Soc. 366, 977-982 (2006)] doesn’t present that compelling a case for a regularity of impacts. And after all, in the paper you previously cited as evidence of the cyclic nature of extinctions [Rohde and Muller, Nature 434, 208 (2005 )], the extinction “cycle” was supposed to be 62 my. You presumed from that study that we are “presently in one now” (i.e. an extinction, since the period is 62 my, and the last one was around 65 mya). However if the extinctions are actually supposed to “cycle” with a 36 my, then we shouldn’t be in an extinction now at all! So which is it?

I suspect the problem relates to the search for “cycles”. The cosmic ray fluxers look at the extinction record and see a 140 my “cycle”; the astrobiologists “see” a 36 my “cycle”; Rohde and Muller “see” a 62 my “cycle”. It’s rather easy to “fit” sinusoidal variations into very sparse data sets (rather few extinction events; rather few impact craters; rather limited fossil record). I don’t have any problem with the possibility that there might be regular variations in the cometary intensity due to passage of the solar system through the plane of the Galaxy. The problem is that the evidence isn't that compelling, and there is really only one extinction event (end-Cretaceous) that has good evidence for a causal impact event.

More compelling (to me!) is the data that focuses carefully on the extinction events themselves to identify features of the contemporaneous geological record to determine potential associated geological and environmental effects. When one does this, the most regular correlate of extinctions is tectonic events (doesn’t necessarily indicate causality of course!). A very recent reanalysis of the argon-argon dating “clock” has established, for example, that the massive Permian Triassic extinction correlates with the massive volcanic events associated with the formation of the Serbian Traps (see Science 25th April 2008)]. The end-Cretaceous extinction (dinosaurs et al) correlates with the tectonic events associated with the Deccan Traps formation. The Paleo-Eocene Thermal Maximum extinctions with the tectonic events associated with the opening up of the North Atlantic at a plate boundary. The Triassic-Jurrasic extinction (201.6 mya) associates with the massive volcanic outpourings of the central Atlantic magmatic province…and so on...

Are these tectonic events governed by grand “cycles”. There’s no evidence for such a cycle, nor is there evidence for any causal attribute of periodicity in these processes.

Actually, when one boils down the essential correlates of extinctions as these are best defined, the evidence indicates that global warming (as the result of the release of greenhouse gases) seems to accompany most extinction events, and that’s one of the compelling reasons for attempting to get to grips with these difficult to study events in the deep history of the Earth!

Thank you for the responses. My personal position is not as extreme as you might believe, in fact its closer to yours than average, I just don't get emotional about it. As I said, we, as a species, have made mistakes by not taking better care of the habitats that we live in and should attempt to correct these mistakes.

I am not saying that the answer is to do nothing, but pointing out that our concentration should be on area that needs it the most like the Amazon deforestation issue.

What I attempted to point out with polar bears is that they are adaptable, they are not actually in danger of extinction while other species are. With limited resources we should concentrate on the species that are both truely endangered and of greater benefit to both ourselves and out habitats. In doing so we will also be helping less endangered species like the polar bear.

Barry Brook is pointing out the endangered areas, of SE Asia. While concerned, I feel we need to look in our own back yards first. By helping the ecology here we can do our small part. This however does not mean that I believe that extinctions over the past 10K years are not natural or that the endangered animals currently under stress were not already under stress, just more so.

I used those 2 articles simply because they were the most recent, not actually the most relavent. As you are aware the idea of extinction cycles is just hypotheses,
while the idea of climate cycles has good evidence. In the case of the KT event, some paleontologists have pointed out that the dinosaurs were in decline from about 70 million years ago due to climate stress. The effect of the Deccan Traps and the Yucatan impact seem to be a fatal blow but most likely not within a cyclic extinction (my view). The PT event also involved an impact and the Siberian Traps but did they actually cause the climate change or again were they a coincidence that simply made things worse?

The issue of clarity in climate cycles is simply that there are too many of them and not all of them identified as yet. Why do ice ages occur? Of the 4 major iceages why are they of different lengths and what causes their end. Are we now coming out of an ice age of merely within an interglacial? There are definate cycles involved but we still have a long way to go in understanding them.

And I agree, Global warming does seem to be directly related to extinctions and I believe that it is the speed not the temperatures that are relavent. The warming slopes are much steeper than the cooling slopes, not allowing enough time for species to adapt.
I simply disagree that mankind is the direct cause. But I feel that our mistakes have only made things worse.

We know reasonably well well why ice ages occur. In the general case, major glacial epochs (we're in one now) are associated with low atmospheric CO2 levels. For example the present glacial epoch began during the Miocene. The early Miocene glacial period around 20 million years ago (mya) is associated with the late Oligocene-early Miocene decrease in atmospheric CO2....the middle Miocene climate optimum (so-called) with a rise of atmospheric CO2, and then the late-Miocene expansion of the East Antarctic ice sheet is associated with a drop in atmospheric CO2 around 14 mya [*****]

Of course these glacial periods also require other factors...for example the Miocene glaciations that heralded the start of the cool period which we're still in, wouldn't have occurred (or at least not to the same extent) without a land mass in the Antarctic for ice to build up on....

Likewise the earliest glacial epoch on Earth more than 3 billion years ago was likely the result of the evolution of the first photosynthetic organisms that produced oxygen which eventually (after turning enormous amounts of oceanic iron salts into iron oxide) destroyed (oxidised) the high methane concentrations that was then "helping" to warm the early Earth.

As for the ice age cycles within the current glacial periods, these are also quite well understood, as I'm sure you know. They result from the slow cyclic variations in the orbital properties of the Earth (google Milankovitch cycles) that result in slow and small variations in the pattern of solar irradiation on the Earth. These cycles have associated variations in greenhouse gas concentrations (especially CO2).

I think it's quite clear that we are in an interglacial period which still has quite a few thousand years to "run".

Abstract: "The Miocene is characterized by a series of key climatic events that led to the founding of the late Cenozoic icehouse mode and the dawn of modern biota. The processes that caused these developments, and particularly the role of atmospheric CO2 as a forcing factor, are poorly understood. Here we present a CO2 record based on stomatal frequency data from multiple tree species. Our data show striking CO2 fluctuations of approximate to 600-300 parts per million by volume (ppmv). Periods of low CO2 are contemporaneous with major glaciations, whereas elevated CO2 of 500 ppmv coincides with the climatic optimum in the Miocene. Our data point to a long-term coupling between atmospheric CO2 and climate. Major changes in Miocene terrestrial ecosystems, such as the expansion of grasslands and radiations among terrestrial herbivores such as horses, can be linked to these marked fluctuations in CO2."

I agree to some extent but feel that CO2 does not play as big a role as you indicate. Its primarily a feedback mechanism and needs something to feedback from, that is why there is a lag to temp increases. Asd you mentioned Milankovitch cycles, these appear to be a major climate driver but not the only one. Then there is the Fairbridge sea level cycles and his last hypothesis about solar (system) cycles, about which Mackey did a paper on after Dr. Fairbridge passed away. AGW is about an artificial CO2 feedback but there is also a very real natural CO2 feedback mechanism.

PS - In my original comment "interesting" was in reference to the potential comments opened up by this particular subject which I am much more familiar with than climate science.

Looks like we did it again"
"'Unintended Consequence'
The decision to place polar bears under the protection of the Endangered Species Act came in response to the continued "loss of sea ice," the bear's natural habitat, that would put them "at risk of becoming endangered in the foreseeable future," according to a statement by the Department of the Interior on May 14.
There is no mention that the danger to polar bears stems from hunting.
In the same statement, Secretary of the Interior Dirk Kempthorne specifically noted that "limiting the unintended harm to the society and economy of the United States" was a concern.
What did not seem to be a priority, however, was the harm to the economy in Arctic Canada, home to about two-thirds of the world's polar bear population, which is estimated at 20,000 to 25,000."
[ABC (US) News]

"Will global warming cause a mass extinction event?" was the title and the simple answer is possibly, dependent on the degree of GW.
The underlying question ( it seems to me) is does it really matter? And if it does in what context?
From an evolutionary viewpoint, no it doesn't, because evolution is a process with only two source drivers, survive and replicate. Everything else is dependent on these.
The process has no ethics, no morals, no compassion, empathy or any other attitude we as humans bring to bear on the issues. And as humans we are often alarmingly double-minded. We worry about the state of one species ( say polar bears) whilst cheerfully killing others in their millions ( mosquitos). Anybody worried about an extinction event that would wipe out mozzies? No, I don't think so.
Any species that dies out creates an opportunity for another to move into that niche and I think we seriously underestimate the ability of lifeforms to adapt to rapid climate changes.
In any event, as I think Quietman said, we are part of the system and driven by the same 'forces' as every other lifeform...survive and replicate. In doing this we may well cause other species to die out, but that is the system.
The dinosaurs ( and maybe a lot of other species)probably died out through their inability to cope with a dramatically altered climate resulting from a major impact event. And so we are here now.
This is one answer from an evolutionary viewpoint.
When we worry about species extinction, changing habitat et al, we need to ask why, and make sure the answer is not coming from a emotional viewpoint.
(Polar bears are nicer than mozzies)

It's interesting that you bring up the relationship between atmospheric CO2 and global temperatures with respect to palaeoclimate.

The Carboniferous and the Ordovician are the only periods in the earth's history when global temperatures were as low as they are today. The late Ordovician was also an Ice Age, while at the same time CO2 concentrations were nearly 12 times higher than they are today (~4400 ppm).

According to greenhouse theory, the earth should have been exceedingly hot.

Obviously, other factors besides atmospheric CO2 have larger impacts on the earth's temperature and global warming.

HealthySkeptic
In addition to the "Ordovician & Silurian" Ice age (Ice Age 2), the Late Carboniferous (Pennsylvanian) was also an ice age (the beginning of the "Pennsylvanian & Permian" ice age or Ice Age 3).

The 'temperatures' for paleoclimate are proxies and need to be treated very cautiously. What does emerge from them is a general cooling trend from Cambrian to present with some 'bumps' along the way (Devonian,Cretaceous, Paleogene). What is obvious from the records, however accurate they may be, is that the earth has experienced far greater climatic changes in the past and LIFE has coped with them all. And some of those changes have been very rapid.
So historically the answer to the topic question is YES.
(but maybe not in the form or abundance we know)

C: "As noted above, it is critical to understand that ecosystems in the 21st century start from an already massively ‘shifted baseline’ and so have lost resilience. Most habitats are already degraded and their populations depleted, to a lesser or greater extent, by past human activities."

Consider the vast changes to the British environment: modern Britain has been transformed in a relatively short period of time from dense woodland/wetlands to what it is now...an 'idustrialised' landscape.
Consider the only bird to have become extinct throughout this process is.........the Great Auk, hunted to extiction.
Wild boar, bears, wolves...hunted to extinction... the list goes on. Nothing to do with climaste or environmental changes.

Mizimi
The single largest issue on carbon capture (and habitat) that I read in the UK papers like the Telegraph or the Times is the deforrestation issue. It is not ssen as easily in the US as it is in the UK and that is a real problem here.

QM:
Humans like quick fixes; they can then forget that problem and move onto the next one ( whatever it might be).
Clearly trees played a big role in sequestering CO2 in the past ( that's how we got coal) so the quick fix is plant more trees and this also has the benefit of increasing habitat space. Unfortunately, many schemes ( such as propagated by the UK Forestry Commission)are monocultural...one genus such as pine is planted because it is fast growing and thus locks up CO2 rapidly.
The short term effect seems good, but in the medium term the soil and local water table suffer dramatically. Studies in the US show up to 13% loss in stream flow within a short radius of plantations and increasing soil imbalance which eventually gives rise to salty soil. Both these effects are detrimental to bio-diversity. The answer is planting a wide mix of trees rather than monocultures....in other words just like Mother Nature did.

Back to the post: We simply have not studied life for long enough to be able to state categorically how it responds to rapid environmental changes ( a bit like climate!!)
We do know there were massive and rapid changes in the past that life coped with..the so called extinction events. Down but not out.
Species evolve/adapt to fill niches: over time that niche alters and if the organism cannot adapt to those changes (whatever the cause) then it dies out because it can no longer compete in that niche.. This is part of the process however much we may dislike it.
Species, by adapting to niches are risking extiction by becoming more and more specialised, yet, with the possible exception of man, this is what all species do.
We should therefore expect to see species decline as a natural part of the overall process. Our effect on local environments may accelerate matters and give certain species a greater problem than they would otherwise have had, but that is part of the 'risk factor' of life itself.
The underlying issue here is what kind of natural world do we want and what are we prepared to give up in order to achieve it? And the answer to that question depends entirely on your perspective.
If you posit that the 'purpose' of evolutionary processes is to produce a species that is capable of adapting to any kind of environment then the logical culmination of that is a species that can colonise ALL possible habitats...including other planets. Only man has that potential through his technology.
If in the process of achieving that goal, the earth is radically impoverished ( from a humanistic viewpoint) does that matter in the overall scheme?

Some food for thought on this subject: Global Warming And Evolution In The Amazon "The results of a new study suggest that past climate changes and sea level fluctuations may have promoted the formation of new species in the Amazon region of South America."

Mizimi
Overall I agree with you. There are even a few species that I would like to see just go away. But as a naturalist I can and do appreciate all species, living and extinct. I just think that extinction is natural and evolution must take it's course. Non-human hominid species for example have been declining since man first evolved. It's not mans intent, it's just nature. Yes, many of the more primitive cultures simply see them as food. Even more primitive cultures see us as food. There are no simple answers or solutions.

Food for thought:
"All flesh is grass" is a Truth. Yet the grasses we rely on for our existence ( grain producers) only appeared in the fossil record around 8mya when CO2 levels were dropping. C4 plants are more efficient photosynthesizers than C3's and release less CO2 back into the air during photorespiration, so over a period of time they reduce atmospheric CO2.
C3 plants ( trees, woody plants et al) 'suffocate' at CO2 levels below 220ppm, and began to decline as grasses took over various habitats until a near extinction event occurred.
Without that event, we would not be here today; arguably (from our point of view) this event was a good thing.
Clearly, if we reduce CO2 levels ( for whatever reason) we need to be aware that it will have deleterous effects on certain species of plants ( and the life forms that feed off them) whereas increasing CO2 will not.
Any temperature effect that may arise from CO2 rises also affects plant life; roughly, a 10C rise in reaction temp causes a 100% increase in reaction mass, so higher temps (within limits) means greater growth and less land areas under cultivation.
[Experiments with grasses indicate a 50% increase in growth @ Co2 levels of 700ppm and a corresponding decrease in lignin - the woody indigestible bits].

["The Carboniferous and the Ordovician are the only periods in the earth's history when global temperatures were as low as they are today. The late Ordovician was also an Ice Age, while at the same time CO2 concentrations were nearly 12 times higher than they are today (~4400 ppm).

According to greenhouse theory, the earth should have been exceedingly hot.

Obviously, other factors besides atmospheric CO2 have larger impacts on the earth's temperature and global warming."]

That's not really correct. One needs to be careful to ensure that the paleoproxies for CO2 and the proxies for cold spells (generally evidence for widespread glaciations) are matched in time. The Carboniferous cold spells cover a massive period (20 million years and close to 70 million years if one extends this through the cold spells of the late Carboniferous and Permian). There are many proxy measures of atmospheric CO2 levels that match these time periods. In other words we know pretty well that the cold periods of the Carboniferous (and Permian) are associated with low atmospheric CO2 levels.

The same unfortunately isn't the case for the very brief late Ordovician cold spell. This "only" lasted a couple of million years, and there isn't so far a proxy CO2 measure that overlaps the cold spell, so we don't know what the atmospheric CO2 levels were. Remember also that the solar constant was around 4% lower than now and so the threshold for cold spells leading to glaciations during this period is considered to be around 3000 ppm of atmospheric CO2 (rather than around 500 ppm of atmospheric CO2 now).

Until we have proxy CO2 measures that we know are "contemporaneous" with the late Ordovician cold spell, we simply don't know whether there is an apparent mismatch between the temperature and greenhouse gas levels.

Notice that the Earth has had many globally cool spells right through late Phanerozoic (several in the Jurassic, Cretaceous and Paleogene and of course in the Neogene). Where there are "contemporaneous" measures of atmospheric CO2 the cool spells match the periods of low greenhouse gas levels rather well (and vice versa - hot/warm spells match high atmospheric greenhouse gas proxy measures).

["The process has no ethics, no morals, no compassion, empathy or any other attitude we as humans bring to bear on the issues."]

Happily, however, we as humans DO have ethics, morals, compassion and empathy, as well as the less emotional abilities to reason, and make valid interpretations about our relationship with the natural world and our impacts, as well as being able to address what we consider to be in the best interests of ourselves and our near, and not so near, descendants. There's no question that the natural world will recover from any large scale trashing of existing environments, either mechanical (habitat destruction/pollution) or via man-made rapid global warming. The question is what sort of a world we wish to live in and leave to those that follow us.

Happily (again!) there are very many intelligent and well-informed individuals and organizations both public and corporate who are taking a clear-headed and rational approach to these very real problems. There aren't too many that hold the ludicrous and repellent "argument" that it's all "natural" and that evolutionary processes will "pick up the pieces" in some far-off future. I suspect the vast majority of individuals are rather more concerned with making mature policy decisions that relate to the next several decades and few hundreds of years, rather than to wash their hands of the issue knowing that several hundreds of thousands and millions of years from now, that a trashed natural environment will have likely recovered.

"as well as being able to address what we consider to be in the best interests of ourselves and our near, and not so near, descendants.".... is not (according to you ("evolution at work").

It should be obvious that mankind has put him/herself outside of the natural evolutionary process to the extent that we are very well able to decide ourselves how things progress in relation to our interaction with the rest of the natural world.

We're not passive participants anymore. We don't have to sit back and wash our hands of the whole business, compelled only by individual immediate self-interest. In fact we'd be horribly irresponsible to take that attitude, and happily the scientists and policymakes are being rather more mature and responsible in adressing these issues.

And of course "The question is what sort of a world we wish to live in and leave to those that follow us."...is not "Emotion at work". What an odd concept. If we decide that we prefer not to have to deal with rising sea levels, increased adverse weather conditions, widespread drought, ocean acidification, destruction of natural habitats and so on, we surely do this based on the most clear-headed and rational grounds.

Chris:
We are all driven by immediate self interest, firstly at the individual level, then at the social/tribal/national levels. We may at times put aside self-interest for the perceived good of the group we are in; that is survival..the first biological imperative.
That is why some nations did not (and probably will not)sign up to protocols intended to stabilise/reduce CO2 emissions...because it was not in their national interests to do so. Regardless of the rationality involved at an academic level.
China 'wants' a western(ised) lifestyle and is achieving that through economic expansion which itself relies on increasing energy usage. China will probably outstrip the US as the prime consumer of fossil fuels within a few years. I do not see China ( or any other developing nation) agreeing to limit fossil fuel usage because others are concerned that the climate may be altered to the detriment of certain life forms ( including man). They will put their (self-perceived)interests first. This is how mankind generally has always acted and probably will continue to do so.
Much as I desire it to be otherwise (emotion again)in this respect I believe I am being pragmatic not stoic.
I agree we can be, and should be, pro-active regarding many problems, (climate included) but inevitably someone is going to get hurt: Who decides that, and what if it turns out to be you that is going to suffer in some way?

And regarding the sort of world we want to pass on to our descendants...who gets to decide that and what ctiteria do they use? Who gets to write the specification that the other 6 billion people on this planet have to comply with, even if it detrimental to their interests? Who decides what species should be preserved and what should not...and on what basis?

The effects you ascribe to AGW are unproven in scale: the models that are used to predict both these events and their scale are incomplete and their predictions should therefore be treated with great caution.

Based on historical evidence, there is a real danger of a future return to a new ice age. So it makes sense to ask what concentration of carbon dioxide would be adequate to stabilize climate so as to extend the current inter-glacial indefinitely. Royer's work gives some idea of the range of concentrations needed. In the paper you cited above, he found that over the Phanerozoic, consistent levels of carbon dioxide below 500 ppmv are associated with the two glaciations of greatest duration... those that occurred during the Permo-Carboniferous some 300 Myr ago and the Cenozoic, within which we are now living.

Cool climates were found to be associated with carbon dioxide concentrations below 1000 ppmv, while no cool periods were associated with concentrations above 1000 ppmv.

Some support for the idea that moderately increased carbon dioxide concentrations could extend the current interglacial period also comes from the work of Berger and Lautre [A. Berger and M. F. Loutre, “An Exceptionally Long Interglacial Ahead?”, Science 297, 1287-1288 (2002).

Working with projections of June insolation at 65 deg. N as affected by Milankovitch variations over the coming 130,000 yrs, they used a 2-dimensional climate model to show that moderately increased carbon dioxide concentrations, coupled with the small amplitude of future variations in insolation, could extend the current interglacial by some 50,000 years. The insolation variations expected over the next 50,000 yrs are exceptionally small and occur only infrequently, the last time being some 400,000 years ago. They also found that a carbon dioxide concentration of 750 ppmv would not extend the interglacial beyond the next 50,000 years. In addition, concentrations of less than 220 ppmv would terminate the current interglacial.

Re #41: You've mixed up "evolution" with "extinction". Evolution does favour species with appropriate adaptations. However extinction events are rather less discriminate in their effects on species survival. Many (perhaps all) of the cataclysmic extinctions in the past are well-associated with marked global-scale warming at a rate that overpowers the adaptability of species. This is what the biosphere faces now, just as in the past.

Re #42: Of course the greenhouse isn't a hypothesis. It's been known since the mid 19th century (since the time of Tyndall and others) that the black body temperature of the Earth is around 30 oC colder than our extant temperature. Without our greenhouse effect there would be no liquid water on the surface of the Earth. That's not a hypothesis. That's a fact. Let's not pretend that we don't know what we do know.

Atmospheric CO2 is a greenhouse gas and contributes to the Earth's warmth. If the atmospheric concentration of CO2 rises, so does the Earth's equilibrium temperature, all else being equal.

Re #43: You're mistaken. Perhaps you haven't read the papaers or are unfamiliar with the science. All of the papers I've cited report independent measures of paleotemperature and paleoCO2. They make no assumptions whatsoever about "the sensitivity" and have nothing to do with "the IPCC".

Yes, as you indicate, the Earth's global temperature is intimately linked with the atmospheric greenhouse gas concentration. As you intimate, that's an inescapable conclusion of an abundant and growing body of science.

However your finishing pondering is rather misplaced. The present massive outpouring of greenhouse gases from our emissions is a concern for the coming decades and few centuries. I think we can leave our descendants of 50,000 years down the road to look after themselves! After all Homo sapiens has only roamed the earth for around 200,000 years, mankind was only just dabbling in the earliest forms of agriculture, animal husbandry and early "permanent" settlements around 20,000 years ago (during the last glacial period, in fact) and recorded civilisation only goes back a few thousand years.

If we look after ourselves and the rest of the biosphere over the next decades and few hundreds of years, there's a pretty good chance that our 50,000-year hence descendants may be in good shape to deal with the next major Milankovitch cycle....

...or maybe not...who can say what might accrue in the vast period of "meantime" between now and then!

Since pretty much all of science and most economists and corporate and government leaders and so on consider that if will be increasingly more damaging to our economies to ignore the problem of massive man-made enhancement of the Earth's greenhouse effect than it will be to mitigate the effects through greenhouse gas emission reduction programmes, it's not really a choice of unknowns.

We know things are going to become increasingly problematic in a warming world (enhanced drought, increased adverse weather effects, rising sea levels threatening massive coastal populations and industrial infrastructure, species extinctions, water restrictions and resulting conflicts and so on).

The point is that global warming is already having adverse effects on many millions of people. So far they're largely the "readily ignorable" in Africa and other low latitude regions where global warming is already enhancing water shortages and agricultural disruption. Addressing this problem by taking mature and rational measures to limit greenhouse gas production, especially by developing and implementing alternative energy sources will benefit everyone. So your notion of choice based on an ill-informed presumption of uncertainty just doesn't accord with the informed view.

And the idea of "deciding which species should be preserved" is also a fallacious one. We recognise that we are impoverished both economically and as human beings as the natural world degrades around us. The aim is to preserve the biosphere to a maximum extent (which is very widely recognised). Witness the efforts to enhance no-fishing zones to preserve ocean biodiversity (and it's obvious economic benefits) and to increase the numer and extent of wildlife preserves. These efforts will only be successful on a large scale if efforts are also made (as they are) in developing the sustainable energy sources that constitute the only possible future for mankind.

So self-preservation also informs us to act rationally to limit our greenhouse gas emissions.

Re: "You've mixed up "evolution" with "extinction"."
Extinction drives Evolution by reducing diversity followed by rapid increases in diversity. I suggest Bob Bakker's book "The Dinosaur Heresies" and Steve Gould's "Wonderful Life" as a good place to start.

Re: "That's a fact. Let's not pretend that we don't know what we do know."
Not factual. It remains hypothetical until proven. It can be demostrated by math but only using assumptions as variables because not all variables have been accurately measured. That is why it was ignored for almost a century.
Sooooo
That's a fact. Let's not pretend that we don't know what we do know.

Re: "They make no assumptions whatsoever"
That is what an argument is. Why would anyone write a paper without an assumption (hypothesis). The GHG hypothesis has been discussed amongst paleontologists for about a hundred years now and has been widely accepted for various extinction hypotheses but we realize that it is a hypothesis and accept it as that.

It certainly won't hurt anything to do so but carried to extremes (read CO2) will hurt everybody. Take action on true pollutants. Acidification of the ocean - control fertilizer runoff for starters. Grow more C4 plants (thanks Mizimi) and stop forest destruction by evacuating southern California so they can;t start the damn fires.

Quietman, you've rather changed the subject in your response. My response in post #44 was to your comment in #41.

But we're getting used to that... Let's switch to your new slant..that extinction drives evolution.

Fine, that's a supportable statement. Stephen Jay Gould's "Wonderful Life" is a decent example. It shows that evolution potentially leads to the flourishing of novel life forms within the "empty" niches that result from major extinctions, as characterised by the Cambrian expansion of forms identified within the Burgess Shale.

But you are resorting again to your dissociated non-humanism: "Wouldn't it be interesting if we had another major extinction....in several hundred thousand or a few million years afterwards what a fascinating diversity of life forms might arise..."

If you want to go there, that's fine. But the rest of us would prefer not to pursue a relentless drive towards the next major extinction. That's not a future that the overwhelming majority of humanity wishes to pursue, however interesting you might consider it.

The fact is that the evidence indicates rather strongly that rapid global scale warming are associated with major extinctions in the earth's history. We can pretend that the greenhouse effect doesn't exist and pursue "interesting" catastrophic scenarios. In real life I suspect that we're going to be rather more mature and rational, and direct our focus onto the coming decades and few centuries (rather than an "interesting" post-extinction potential diversification some millions of years in the future).

Re the greenhouse effect:

I'm afraid the greenhouse effect is a fact Quietman. Our (sciences's) understanding of the world is not defined by one individuals ignorance.

Re "assumptions" and the "IPCC"

You've got that wrong again. You've said something in your post #43 that simply isn't true. If one has to contrive untruths and then pursue these to attempt to make a point, then the point is really not worth making, is it.

To reiterate, the work described in the papers/reviews I cited in my post #35 make no assumptions whatsoever about the supposed "climate sensitivity" or any supposed "hypotheses" of the IPCC.